Refried Bean Tortilla Cake

Well, whodathought that the recipe I have referred to for years as "that baked thing with tortillas and refried beans" had a name?  Nigella calls a similar recipe 'Mexican Lasagne'.  Whatever, this has been an old favourite for a long time - cheap, veggie, filling and delicious.  However, a plea - do NOT use tinned refried beans which smell, look, and probably taste like dog pooh.  Your own will be so much nicer.  For 2, fry an onion and then stir in a large tin of drained, rinsed kidney beans.  Another plea: try to get the 'East End' brand - brilliant, soft mealy beans, and only 49p a can.  Their chickpeas are the best too.  Now, use a wooden spoon to mash the beans into the pan with the onion, so as many break up as possible.  Add a teaspoon each of ground cumin, paprika, chilli powder (or to taste) and dried oregano.  Now add half a large tin of tomatoes - or a small tin! - and the same in volume of water.  Add salt if liked and stir an mash until the mix has reduced.  Now, simply layer up between flour tortillas with grated cheese - I used 4 tortillas - and put cheese on the top.  Bake for about 15 minutes and serve in quarters.  This quantity should really serve four, but we are greedy pigs and eat the whole lot.